Cities with large Latino populations and high economic inequality are also least likely to have policies in place directing police officers about how to treat people they suspect of being undocumented immigrants, according to a new study.

The researchers also found that in cities which were highly segregated in terms of where Latino populations lived, the police were most likely to voluntarily cooperate with federal immigration authorities.

This finding builds on prior research which suggests that majority group members are more likely to attribute negative stereotypes and are more fearful of minorities when they live in highly segregated communities. As a result, local police forces tend to respond to such majority group fears and sentiments with greater support for aggressive crime-control measures.

How individual police forces treat those that they suspect of being illegal immigrants varies greatly from one city to the next in the US.

In Albuquerque, New Mexico, the police department has a policy that states clearly, “Officers shall not stop, question, detain, or arrest any person on the ground that they may be undocumented and deportable foreign nationals.” But this is unusual. Local police departments across the US have become increasingly involved in enforcing federal immigration laws since the mid-1990s.

For the study, researchers Jason Carmichael from McGill University and Stephanie Kent from Cleveland State University looked at data from 160 cities across the country with populations of over 100,000 for the period between 2000-2007.

What are the implications?

The researchers believe that:

When local police get involved in the enforcement of immigration laws it can degrade public trust in law enforcement, particularly within targeted communities. Scholarship has pointed to a number of consequences associated with a decline in confidence. These include a lower probability of informing police when criminal activity is taking place, a lower probability of cooperating with an ongoing police investigation, and less willingness to act as a witness or informant.

Under such circumstances, targeted communities often see an uptick in violence or other forms of victimization as some individuals will take advantage of the decreased likelihood of residents reporting criminal activity. This is particularly the case for those who are either illegal themselves or who have family members that are not in the country legally.

The researchers add that despite President Donald Trump’s calls for greater cooperation between federal immigration officials and local law enforcement, there has been little change in how police respond to those they suspect are in the country illegally. This is likely the case because US Presidents have little or no control over local policing policies and practices.

“For decades, candidates in federal elections have campaigned on a crime-control agenda but once in office discover that such issues are largely out of their control given that law enforcement practices and priorities are primarily established by city officials,” says Jason Carmichael, who teaches in the department of sociology at McGill University.

“Thus, the Trump administration can say all they want to city managers about how they should treat non-citizens (e.g. turn them over to federal immigration officials) but there is nothing compelling cities to comply with such directives. Local compliance is almost entirely voluntary.

“What we’ve identified is that city officials are more inclined to comply when they have a large, residentially segregated Latino population,” Carmichael says.